immediately, and the operator is aware of his mistake. Once the finished prosthesis is permanently affixed over correctly seated implants, a positive prognosis usually results.

Amid the confusion and often imperfect results, why persist? Thousands of former dental cripples who now enjoy successful implant-supported prostheses are grateful that we have. Hopefully as more practitioners become interested in implantology, their skill, energy, and intelligence will minimize errors and improve the overall prognosis.

Today failures can be reduced by critically evaluating current implant designs and discarding the impractical. Failures from inexperience will understandably persist as novice operators learn the skill, and should not be confused with failures from bad design. Clearly it is time for the critics to commit themselves to indepth investigations of the various implant designs, implant histology, and the sophisticated prosthodontics required by implant insertion. Broad condemnations are neither fair nor adequate.

Implantology will probably always be limited to relatively few practitioners. It is cross-disciplinary; requiring a wide range of surgical and prosthodontic skills that are usually specializations in themselves. However, whether or not the practitioner wishes to become an implantologist himself, he should at least understand its principles and applications in order to expand his patient's prosthodontic alternatives.

Maxillary implantation beautifully illustrates the potentials and dangers inherent in implantology, and for this reason it has been chosen for the initial volume in this series. What has happened within the past three years in maxillary implant design summarizes many of the frustrations implantologists have historically faced, and demonstrates how a fertile idea can evolve into a satisfactory conclusion.

The maxillary implantation story is dominated by the adverse influence of nondental anatomy. Sinus expansion hinders the use of the bladevent, which can be highly successful elsewhere in the mouth, and makes it risky to position a subperiosteal implant's bar or strut over the fragile bone separating the sinus from the oral cavity. The pterygoid extension implant, from the moment of its inception, obviously contained the seeds of a solution. This implant's refinement into more practical, wider applications exemplifies the more rewarding aspects of implantology.

The designs and procedures set forth in this book are my own. This does not infer that the work of certain other practitioners is not equally valuable. It is simply that in a catalog of everyone's work I can-not hope to convey my own personal sense of satisfaction with dental implants.

xx